The present invention relates generally to methods and apparatus for cleaning thin discs, such as semiconductor wafers, compact discs, glass substrates and the like.
A conventional method for cleaning particles from semiconductor wafers is known as megasonic cleaning. During megasonic cleaning, a transducer oscillates between compressed and strained states at or near a megahertz rate (e.g., at a xe2x80x9cmegasonicxe2x80x9d rate). The transducer is coupled to a cleaning fluid; either cleaning fluid in a fluid filled tank, or cleaning fluid flowing through a nozzle. The megasonic oscillation of the transducer is thereby coupled to the fluid, causing a megasonic pressure oscillation therein. As the pressure in the cleaning fluid oscillates between positive and negative, cavitation or bubbles form in the cleaning fluid during negative pressure and collapse or shrink during positive pressure. This bubble formation/collapse gently cleans the surface of a wafer submerged in the cleaning fluid. Specifically, bubble implosion near the surface of the wafer helps to remove articles from the wafer and thus has a positive effect on cleaning efficiency.
One drawback of conventional cleaning methods is that bubbles in the cleaning fluid that are not near the wafer""s surface may scatter energy transmitted by the transducer and thus cause a decreasing power density along the surface of the wafer as the distance from the transducer increases. Therefore, a wafer is typically translated or rotated during cleaning so that uniform megasonic energy scans the entire surface of the wafer. Wafer supports typically are used to rotate a wafer and to support the wafer during cleaning. However, contact between the moving wafer and the moving wafer supports may generate particles and/or damage the wafer during cleaning. Further, moving parts (e.g., rotating wafer supports) may be expensive to maintain and may require regular maintenance. As well, most conventional wafer supports block a portion of the megasonic energy generated by a transducer. Accordingly, a need exists for improved methods and apparatus for cleaning a thin disc such as a semiconductor wafer.
To overcome the drawbacks of the prior art, methods and apparatus are provided for cleaning a thin disc. In accordance with a first aspect of the invention, an apparatus is provided that includes a tank adapted to contain a fluid, and at least one support mechanism adapted to support a thin disc such that the thin disc is at least partially submerged in the fluid. The apparatus further includes a plurality of transducers each adapted to produce energy waves in the fluid, and a controller adapted to adjust the energy waves produced by each transducer so as to scan an energy wave maximum along a surface of a thin disc supported by the at least one support mechanism.
Other features and aspects of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawings.